Efficiency of nitrogen,phosphorus, and potassium use by corn,sunflower, and sugarbeet for the synthesis of organic matter

Summary A three-year experiment was conducted in natural conditions on chernozem soil to examine the efficiency of nitrogen, phosphorus, and potassium use by corn (C₄ type), sunflower and sugarbeet (C₃ type) grown in optimum conditions of mineral nutrition (N₁₀₀P₁₀₀K₁₀₀ kg/ha). Plant materials were analysed for the concentration of nitrogen, phosphorus, and potassium and dry matter mass per individual plant parts and the whole plant.Leaves of different age, of all three plant species, were analysed to find eventual differences in the efficiency of use of nitrogen, phosphorus, and potassium in the synthesis of organic matter depending on leaf age.It was found that corn had the lowest concentration of the elements studied but the highest dry matter mass. In other words, corn was more efficient than sunflower or sugarbeet in the use of these elements for the synthesis of an organic matter unit. Such results were arrived at in both sets of analyses, i.e., the analyses of leaves performed in the course of ontogenetic plant development as well as the analyses of leaves of different age.     

Control of plant growth by nitrogen: differences between cereals and broadleaf species

Abstract. In four dicotyledonous species low levels of N strongly inhibited leaf expansion during the day but had little or no effect at night. In contrast, daytime and night-time expansion were equally affected in four cereal species. The results support the general concept that in dicotyledons, N controls leaf expansion through its effects on hydraulic conductivity. In such N-limited plants, water deficits generated by transpiration may inhibit daytime cell expansion. In cereals, cell expansion and transpiration occur in separate zones of the leaf and are apparently unrelated.
Growth analysis showed that low levels of N inhibited leaf area growth more strongly in dicotyledons than in cereals, but had similar effects on net assimilation rates of plants in the two groups. As a result, dry matter production was more efficient in cereals than in dicotyledons when N was limiting.     

Direct and indirect effects of light on stomata II. In Commelina communis L.

Abstract. Two experiments are described which test the normal correlations that arise between stomatal conductance, net CO₂ assimilation rate, and intercellular CO₂ concentration (C_i), using whole shoots of Commelina communis L. In the first, conductance increased with decreasing C_i, at four different quantum flux densities, such that there was no unique relationship between conductance and quantum flux density or C_i, In the second, conductance increased hyperbolically with increasing quantum flux density while C_i was held constant at 466, 302, and 46 μmiolmol⁻¹, and the response differed at each C_i. In neither experiment was conductance consistently related to net CO₂ assimilation rate in the mesophyll. In both experiments high C_i suppressed the response of conductance to light, while there was a large response of conductance to light at low C_i, indicating an interaction between the effects of light and CO₂ on stomata. The results show that the parallel responses of assimilation and conductance to light result in constant intercellular CO₂ concentrations, and not that stomata maintain a 'constant C_i'.     

A precise potentiometric method for determination of algal activity in an open CO2 system

Abstract. The activity of the green alga Scenedesmus obliquus was studied in simplified nutrient solutions (20 mol m₋₃ NaNO₃, 20 mol m₋₃ NH₄C1, 20 mol m₋₃ NH₄NO₃, and 20 mol m₋₃ NaCl, respectively) at 25 °C. The experiments were performed under welldefined incident photon density fluxes ranging from 10 to 200 μmol m₂ s₋₁, Light-dependent changes in pH and alkalinity (A) were followed by means of a potentiometric method using a glass electrode. In the experiments, carbon dioxide with known partial pressure was bubbled through the algal suspension, and during dark periods ul intervals of 1 h, the solution was allowed to equilibrate with the gas phase. This technique was applied to calculate equilibrium values of pH and alkalinity at regular intervals during a 12-h period. Results obtained in NaNO₃, solution show a linear increase in A with time, at each level of illumination studied. After an initial drop, A also increases in NH₄NO₃, solution in a similar way to that in NaNO₃ solution. The change in A with time was also found to increase linearly with the photon density flux studied and no saturation level could be defined. In experiments in NaCl solution, no changes in A were registered while measurements in NH₄Cl solution showed a decrease in A with time.     

Effects of tannins on growth and digestion in two species of papilionids

The effects of tannins on growth and digestion were compared in two species of swallow-tail caterpillars — Papillio polyxenes, a specialist on Umbelliferae that normally does not encounter tannins in nature, and P. glaucus, a generalist whose hostplant range includes tanniniferous tree species in several families. In one experiment, tannin extracted from Liriodendron tulipifera, a P. glaucus foodplant, was applied to leaves from hostplants on the two species; tannin in the diet caused greater mortality in P. polyxenes but failed to do so in P. glaucus. In a second experiment, tannins did not affect digestion, growth rate or nitrogen utilization in either species over a 24-hour period. These findings are inconsistent with the proposed mechanism of digestibility reduction by tannins and, moreover, demonstrate that some degree of counteradaptation is possible in coevolved species. Tannins may thus possess toxic properties other than digestibility reduction.

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Résumé La comparaison a porté sur les effets des tanins sur la croissance et la digestion de deux espèces, Papilio polyxenes, spécialiste d'Ombellifères qui ne rencontre pas normalement de tanins dans la nature, et P. glaucus, généraliste dont les plantes hôtes comprennent des espèces d'arbres tanifères de plusieurs familles. Dans une expérience, des feuilles de plantes hôtes des deux espèces ont été traitées par du tanin extrait de Liriodendron tulipifera, consommé par P. glaucus; ce tanin dans l'aliment a provoqué une forte mortalité chez P. polyxenes mais a été sans effet sur P. glaucus. Dans une second expérience, les tanins n'ont pas modifié la digestion, le taux de croissance et l'utilisation d'azote par ces espèces pendant une période de 24 heures. Ces résultats ne concordent pas avec les mécanismes de réduction de la digestibilité envisagés pour les tanins, et, par ailleurs, démontrent qu'un certain degré de contreadaptation est possible chez des espèces ayant coévolué. Les tanins peuvent alors posséder quelques propriétés toxiques différentes de la réduction de la digestibilité.

     

The effect of temperature,irradiance and animal size on incorporation rates of Simocephalus vetulus

Carbon incorporation rates of Simocephalus vetulus were measured to study the effects of the physical state of the animals, size of the animal, varying temperature and light conditions. Physical state of the animal showed little effect on incorporation rates after the first hour. Incorporation rates increased in proportion to the third power of animal size. Experimental animals collected at temperatures of 12, 20 or 25°C fed maximally at 10, 15 and 25°C respectively, when subjected to a feeding temperature range of 5 to 30°C. We have interpreted this as an indication that S. vetulus is able to acclimate and incorporate maximally at various temperatures after prolonged exposure to that temperature. When fed over an irradiation range of 0 to 4.68 × 10^–3 cal cm^–2 s^–1 incorporation rates were indirectly proportional to irradiance. This suggests a response to decreased irradiance in the weedy, littoral habitat of these animals.     

Respiration of different stages and energy budgets of juvenile brachionus calyciflorus

Respiration data for different stages of Brachionus calyciflorus, fed with three concentrations of Kirchneriella lunaris at 20°C, are presented. Increasing oxygen consumption from 4.1 to 4.6 .10^–3 µl/h × ind. with food decreasing from 5.10⁶ to 10⁶ and 4.10⁵ cells/ml has been fourid for adult females with one egg, but other age groups showed divergent results. Based on the respiration data for age groups o to 12 and 12 to 24 h old and some other results and calculations-e.g. dry weight and caloric content of eggs and females, ingestion rates/h for the different concentrations of food-energy budgets for juvenile, growing B. calyciflorus are presented.     

Acetate thiokinase and the assimilation of acetate in Methanobacterium thermoautotrophicum

Methanobacterium thermoautotrophicum growing on H₂ plus CO₂ as sole carbon and energy source was found to contain acetate thiokinase (Acetyl CoA synthetase; EC 6.2.1.1): Acetate+ATP+CoA Acetyl CoA+AMP+PPi. The apparent K _m value for acetate was 40 M. Acetate kinase (EC 2.7.2.1) and phosphotransacetylase (EC 2.3.1.8) could not be detected. The specific activity of acetate thiokinase was high in cells grown with limited H₂ and CO₂ supply (approximately 100nmol/min · mg protein), it was low in exponentially grown cells (2 nmol/min·mg protein). This corresponded with the finding that cells growing linearly in the presence of acetate assimilated the monocarboxylic acid in high amounts (>10% of the cell carbon was derived from acetate), whereas exponentially growing cells did not (<1% of cell carbon was derived from acetate). These latter observations indicated that acetate thiokinase and free acetate are not involved in autotrophic CO₂ fixation in M. thermoautotrophicum. The presence and some kinetic properties of succinate thiokinase (EC 6.2.1.5), adenylate kinase (EC 2.7.4.3), and inorganic pyrophosphatase (EC 3.6.1.1.) are also described.     

Short-term ammonium inhibition of nitrate utilization by Anacystis nidulans and other cyanobacteria

Ammonium at low concentrations caused a rapid and effective inhibition of nitrate utilization in the light by the cyanobacterium Anacystis nidulans without affecting the cellular level of nitrate reductase activity. The inhibition was reversible, and the ability of the cells to utilize nitrate was restored immediately after ammonium had been exhausted. The inhibitory effect was dependent on consumption by the cells of the added ammonium which was rapidly incorporated into amino acids. In the presence of L-methionine-d,l-sulfoximine (MSX) or azaserine, inhibitors of the glutamine synthetase-glutamate synthase pathway, ammonium did not exhibit any inhibitory effect on nitrate utilization. Ammonium assimilation, rather than ammonium itself, seems to regulate nitrate utilization in A. nidulans. Short-term inhibition by ammonium of nitrate utilization and its prevention by MSX were also demonstrated in the filamentous cyanobacteria Anabaena and Nostoc.Abbreviations MSX L-Methionine-d-l-sulfoximine     

Nitrogen limitation and recovery in the cyanobacterium Aphanocapsa 6308

The effects of nitrogen limitation and recovery on nitrogen-containing macromolecules were followed in the cyanobacterium Aphanocapsa 6308. Removal of nitrogen from growth media triggers the degradation of the endogenous nitrogen reserves phycocyanin and cyanophycin granule polypeptide in the cyanobacterium Aphanocapsa 6308. Nitrogen recovery involves immediate synthesis of cyanophycin granule polypeptide with peak levels of 5–12% of cell dry weight found 8–12 h after a utilizable nitrogen source is added. A rapid decrease in cyanophycin granule polypeptide level then occurs and the level remains low even in light-limited stationary growth with all nitrogen sources tested except nitrate and ammonia. Protein and phycocyanin recoveries began 3 h after a utilizable nitrogen source was added. Data suggest continuous activity of the enzyme system synthesizing cyanophycin granule polypeptide in nitrogen-limited cells, but synthesis of a degrading system only after nitrogen recovery begins.Nonstandard Abbreviations CGP Cyanophycin granule polypeptide - CAP chloramphenicol - PC phycocyanin To whom offprint requests should be sent